Alisa Sivak, MA, DipEd

Alisa assists the Centre for Contact Lens Research by writing and editing publications, reports, grant applications, and educational communications.

Brian Tighe reviewed the development of silicone hydrogel lenses, including their significant market growth since 1998, the shift from continuous wear (CW) to both overnight and daily wear (DW) use, the development of technology able to increase the availability and lower the cost of these lenses, and the development of a number of new silicone hydrogel materials in recent years.

Clinical trials

Carol Lakkis and Kate Weidemann (University of Melbourne) reported that over 12 months of 30-day CW, comfilcon A was comparable to lotrafilcon A and balafilcon A in terms of performance, but with significantly fewer adverse responses and higher comfort ratings. Robert McIlroy and colleagues (Brennan Consultants) conducted a separate study from which they reported that comfilcon A performed significantly better than lotrafilcon A and balafilcon A, particularly in terms of comfort and vision.

Graeme Young and colleagues (Visioncare Research) tested the effects of refitting
‘problem’ patients with senofilcon A lenses. A majority of subjects had significant improvements in signs and symptoms, including dryness, comfort, hyperemia and staining.

Bill Long and colleagues (CIBA) reported the results of a 3-year, multi-site trial assessing the performance of lotrafilcon A lenses, including long-term improvements in corneal health and symptoms as well as a decrease in myopia progression. In the same study, neophytes dispensed DW lenses replaced every two weeks showed no improvements in biomicroscopy signs and symptoms, and did show an increase in myopia progression.

Evaluating the performance of investigational lotrafilcon B toric lenses and balafilcon toric lenses for EW, Kathy Dumbleton and colleagues (CCLR) confirmed that silicone hydrogel lenses for astigmatism can be worn successfully on an overnight basis. In a 117-site, 629-patient study, William Reindel and colleagues (Bausch & Lomb) found that the performance of balafilcon torics is superior to that of conventional hydrogel torics, with minimal rotation, better visual acuity, and higher comfort.

Galyfilcon A and alphafilcon A toric lenses were worn successfully over a 2-week period by subjects in a multi-site study conducted by Simone Bayer and Graeme Young (Visioncare Research). Fifty percent of subjects with previous spherical lens experience rated toric lens comfort as ‘very good’ or ‘excellent’ at the follow-up visit; their VA was on average nearly one line better than VA with their habitual spherical lenses.  

Tears, wettability and comfort and dryness

Lyndon Jones (CCLR) led a symposium discussing the interface between tears and silicone hydrogel lenses, resulting from the unique material properties of these lenses. Though these lenses allow more oxygen to reach the eye, they are 2-4 times stiffer than conventional lenses, which can lead to mechanical complications. The addition of silicone also renders these lenses more hydrophobic. He noted the importance of understanding the lens interaction with the tear film, particularly in terms of surface wettability and in-eye deposition.

Jason Nichols and Ewen King-Smith (Ohio State University) found that post-lens tear film thickness associated with silicone hydrogel lens wear is similar to that found with hydrogel lens wear, but that silicone hydrogels are associated with higher rates of post-lens tear film thinning.

Bill Long and colleagues (CIBA) described the results from 5 trials investigating refitting 1279 adapted wearers of non-silicone hydrogel lenses with silicone hydrogel lenses. When refitted with lotrafilcon A and B, subjects reported significant improvements in dryness, both during the day and at the end of the day. In contrast to these findings, Noel Brennan (Brennan Consultants) described the results of a retrospective investigation consisting of 334 individual wearing trials by 184 different subjects wearing 6 contact lens brands. He reported that balafilcon A, etafilcon A, lotrafilcon B lenses did not alleviate end-of-day discomfort compared to conventional DW hydrogels.

David Meadows and colleagues (Alcon) reported that OptiFree® Replenish™ provided the best wettability with silicone hydrogel lenses (lower mean wetting angle) when compared to Renu® Multiplus® and Renu® with MoistureLoc™.  Carole Maldonado-Codina and Philip Morgan (University of Manchester) used a sessile water drop technique to investigate the in vitro wettability of silicone hydrogel lenses. Contact angles were higher in saline-soaked lenses compared to lenses measured straight from the packaging solution.  Nancy Keir and colleagues (CCLR) reported that comfilcon A lens showed excellent wettability and comfort, factors that appear to be related. Comfilcon A lenses had lower contact angles than balafilcon A lenses.

Deposits and solutions

Fiona Carney and colleagues (CIBA) reported that lotrafilcon A and B lenses pre-soaked in either a cholesterol or lysozyme solution did not adsorb significant amounts of lipid compared to unsoaked lenses, whereas pre-soaked balafilcon A, galyfilcon A, senofilcon A and etafilcon A lenses adsorbed substantial lipid. Etafilcon adsorbed the most lysozyme of all the lenses evaluated, and balafilcon adsorbed more than the other silicone hydrogel lenses.

The CCLR also presented a number of studies relating to the interaction between silicone hydrogel lenses and the tear film. Mary Ann Glasier and colleagues reported on their success using a novel method to examine the quantity and conformation of lysozyme deposited on galyfilcon A. Using novel, low acid strength buffers to extract lysozyme from in vitro doped galyfilcon lenses, they confirmed that these lenses attract very low amounts of denatured lysozyme, similar to other surface-treated silicone hydrogel materials, though the lysozyme is more active than that found on lower water content silicone hydrogel materials, such as lotrafilcon. The same group noted that lotrafilcon A lenses adsorb the least amount of lysozyme deposits, with the lowest amount of activity, whereas they found the highest accumulation of lysozyme on conventional hydrogels: etafilcon and omafilcon. Etafilcon also had the highest lysozyme activity.

A group led by Lakshman Subbaraman (CCLR) used radiochemical analysis to compare the kinetics of lysozyme deposition on lens materials, finding that this depends on the chemical structure of the lens material. Deposition occurs rapidly with etafilcon A lenses before reaching a maximum, while silicone hydrogel materials (as well as Group I, II and PMMA materials) progressively accumulate lysozyme, with no plateau.

Feng Zhang and colleagues (CCLR) used a radio-labelled lysozyme technique to measure the amount of lysozyme left on lenses after exposure to a variety of care regimens. They reported no marked difference between care regimens, but galyfilcon A was most easily cleaned of lysozyme deposits, possibly as a result of its more hydrophilic surface. 

Measuring contact angles, Holly Lorentz and colleagues (CCLR) found that the wettability of balafilcon A, galyfilcon A and senofilcon A lenses were unaffected by lipid, while some surface-treated silicone hydrogel materials (lotrafilcon A and B) exhibit markedly reduced contact angles after exposure to lipid. These results may help to explain why certain silicone hydrogel materials improve in comfort during the first few hours or days of wear.

Mark Wilcox and colleagues (IER, Vision CRC) quantitatively identified and compared the proteins and lipids extracted from lotrafilcon B and galyfilcon A contact lenses worn on a DW basis. Less protein was found to be deposited on the lenses that had been cleaned with a hydrogen peroxide-based solution. Higher levels of cholesterol were found on galyfilcon lenses, and in higher quantities than was found on lenses that had been cleaned with a TCA solution (tectronic 1304, citrate and AMP095).

Certain combinations of contact lens materials and care systems are known to produce staining. After a series of studies testing 12 lens-care system combinations, Christopher Amos (CIBA Vision), Graeme Young (Visioncare Research Ltd.) and Carol Lakkis (Clinical Vision Research) reported that generalizations can not be made about lens care preservatives, as the interaction between preservatives and silicone hydrogels is combination-dependant.

Ralph Stone and colleagues (Alcon) reported that the company’s latest polyquad-based solution produces significantly less severe corneal staining and higher comfort scores, particularly for symptomatic subjects, when compared with a number of other lens care solutions, including three PHMB-based solutions.